His name is John Harrison and he is sort of an average – that is what makes him so scary – he is just an average guy who works in an organization called Starfleet, and he turns against the group because he has got this back-story and this kind of amazing secret agenda. After two very violent attacks, one in London and one in the US, our characters have to go after this guy and apprehend him. And it is a far more complicated and difficult thing then they ever anticipated.

Cumberbatch wrote:

He’s sort of superhuman, pretty much unbeatable. Brainy and brawny. He manipulates situations. He’s incarcerated when Kirk is talking to him and yet he still gets Kirk to do his owrk for him. He pushes him into a corner where the only route to salvation is cooperation. There is a real Hannibal Lector quality to him.

Oh yeah, let me guess. They catch him, and then he's in his cell and it turns out he actually wanted to get caught in his evil plan, and THEN things turn really ugly and he escapes again.